Method and system for start and operation of an electrically driven load

Abstract

A method and system for starting and operating an electrically driven load, e.g. a compressor or pump, by power supply from a mechanical driver, e.g. a turbine or combustion engine, whereby the load is mechanically connected to a first electrical machine, and the mechanical driver is mechanically connected to a second electrical machine. The first electrical machine is electrically interconnected to the second electrical machine at a standstill or when the first and or second machine have low speed. In an acceleration phase, the first electrical machine is accelerated by accelerating the second electrical machine with the mechanical driver. When the first electrical machine has reached a predefined rotational speed, the first machine is synchronized with a local electrical power network and connected it to that network.

1. A method for starting and operating an electrically driven load by power supply from a mechanical driver, the method comprising:
 the load mechanically connected to a first electrical machine in a power range of 10 MW and above; 
 said mechanical driver mechanically connected to a second electrical machine; 
 electrically interconnecting the first electrical machine to the second electrical machine at a standstill or when at least one of the first machine and the second machine have low speed, whereby the connection of the second electrical machine is dedicated to the first electrical machine; 
 in an acceleration phase, accelerating the first electrical machine by accelerating the second electrical machine with the mechanical driver; and 
 when the first electrical machine has reached a predefined rotational speed, synchronizing the first electrical machine with a local electrical power network and connecting it to the network. 
 
     
     
       2. The method according to  claim 1  wherein the local electrical power network is powered from an external power network. 
     
     
       3. The method according to  claim 1  wherein the local electrical power network is powered by electrical machines driven by at least one turbine. 
     
     
       4. The method according to  claim 1  wherein the mechanical driver comprises a steam turbine, and that the acceleration phase comprises starting the steam turbine at or near zero speed. 
     
     
       5. The method according to  claim 1  further comprising in the acceleration phase, accelerating the first electrical machine from zero speed as an induction motor by controlled energizing of the second electrical machine driven by a gas turbine operated at its minimum speed. 
     
     
       6. The method according to  claim 1  wherein the acceleration of the second electrical machine is provided by accelerating a gas turbine running from its minimum speed and up the rated speed, while being mechanically coupled to the second electrical machine. 
     
     
       7. The method according to  claim 1  further comprising operating a single or a plurality of fixed speed electrical drives in a segregated power system with variable system frequency in order to adapt to process variations and flow or capacity control requirements, independent of the utilities from a system with fixed frequency. 
     
     
       8. A method of starting and operating an electrically driven subsea load by power supply from a mechanical driver comprising:
 the subsea load mechanically connected to a first electrical machine; 
 the mechanical driver mechanically connected to a second electrical machine; 
 electrically interconnecting the first electrical machine to the second electrical machine at a standstill or when at least one of the first machine and the second machine have low speed, whereby the connection of the second electrical machine is dedicated to the first electrical machine; 
 in an acceleration phase, accelerating the first electrical machine by accelerating the second electrical machine with the mechanical driver; and 
 when the first electrical machine has reached a predefined rotational speed, synchronizing it with a local electrical power network and connecting it to the network. 
 
     
     
       9. A start and operation system for the starting and operating of at least one mechanical load; the system comprising:
 the load connected to and driven by at least one first electrical machine in a power range of 10 MW and above; 
 power to the first electrical machine is provided with a mechanical driver which is mechanically connected to a second electrical machine functioning as a generator; 
 the second electrical machine adapted to be electrically connected to said first electrical machine or a plurality of first electrical machines, whereby the system is adapted to accelerate said first electrical machine(s) by controlled delivery of power from the second electrical machine to the first electrical machine. 
 
     
     
       10. The system according to  claim 9  wherein the mechanical driver comprises a steam turbine, and that the system is adapted to accelerate the first electrical machine by starting the mechanical driver and second electrical machine from zero or near zero speed. 
     
     
       11. The system according to  claim 9  wherein the mechanical driver comprises a gas turbine connected to the second electrical machine, and that the system is adapted to accelerate the first electrical machine from zero or low speed by controlled energizing of the second electrical machine with the gas turbine. 
     
     
       12. The system according to  claim 11  wherein the acceleration of the second electrical machine is provided by accelerating a gas turbine running from its minimum speed and up the rated speed, while being mechanically coupled to the second electrical machine. 
     
     
       13. The system according to  claim 9  further comprising an electric power transmission network for interconnection of first and second electrical machines, the network comprises at least a double bus bar or at least a double circuit breaker system to enable parallel utilization of other electrical equipment independent of the actions of the second electrical machine for starting the first electrical machine. 
     
     
       14. The system according to  claim 13  wherein the power transmission network comprises at least two bus bars adapted to operate at least two different frequencies. 
     
     
       15. The system according to  claim 9  wherein the first electrical machine comprises one or more electrical synchronous machines and/or induction machines. 
     
     
       16. The system according to  claim 9  wherein the second electrical machine comprises an electrical synchronous machine. 
     
     
       17. A start and operation system for the starting and operating of at least one mechanical subsea load, the system comprising:
 the subsea load connected to and driven by at least one first electrical machine; 
 power to the first electrical machine provided with a mechanical driver which is mechanically connected to a second electrical machine functioning as a generator; 
 the second electrical machine adapted to be electrically connected to said first electrical machine or a plurality of first electrical machines, whereby the system is adapted to accelerate said first electrical machine(s) by controlled delivery of power from the second electrical machine to the first electrical machine.